1. Field of the Invention
The present invention relates to dielectric ceramic compositions suitable for use in high frequency regions, for example, microwave and milliwave regions. More specifically, the present invention relates to dielectric ceramic compositions suitable for miniaturization by laminating and co-sintering with metal electrodes, and to ceramic multilayer substrates, ceramic electronic parts and laminated ceramic electronic parts using the dielectric ceramic compositions.
2. Description of the Related Art
In recent years, high frequency dielectric ceramics have been widely used in, for example, dielectric resonators and MIC dielectric substrates. In order to miniaturize high frequency dielectric ceramics, it is required that the dielectric constant be large, the Q value be large and the temperature dependency of the dielectric constant be small.
An example of high frequency dielectric ceramic compositions is disclosed in Japanese Examined Patent Application Publication No.4-59267. Herein, the dielectric ceramic composition is represented by the general formula (Zr, Sn)TiO4. This dielectric ceramic composition is fired at a high temperature of 1,350xc2x0 C. or more to provide a relative dielectric constant xcex5r of 38 or more and a Q value of 9,000 or more at 7 GHz.
Generally, in dielectric resonators, etc., used in high frequency regions, it is necessary to use low resistance and inexpensive metals such as Ag and Cu, as electrodes. In order to co-sinter the metal and the ceramic, the ceramic must be fired at a temperature below the melting points of these metals.
The melting points, however, of the aforementioned metals are 960 to 1,063xc2x0 C., which are extremely low compared to the 1,300xc2x0 C. firing temperature of the aforementioned dielectric ceramic composition. Accordingly, there is a problem in that the aforementioned dielectric ceramic composition is suitable for use in high frequencies, but cannot use these metals as inner electrode materials.
Regarding the dielectric ceramic composition disclosed in the aforementioned Japanese Examined Patent Application Publication No.4-59267, the firing temperature is as high as 1,350xc2x0 C. or more. Therefore, the dielectric ceramic composition could not be co-sintered with the aforementioned low resistance metals.
The object of the present invention is to provide a dielectric ceramic composition which can be fired at a temperature of about 1,100xc2x0 C. or less, can be co-sintered with low resistance metals such as Ag and Cu, has a high dielectric constant, a high Q value and has a small temperature coefficient of the dielectric constant, and therefore is superior in high frequency characteristics, and exhibits high reliability in its environmental tolerance characteristics.
Another object of the present invention is to provide a ceramic multilayer substrate, a ceramic electronic part and a laminated ceramic electronic part which use the aforementioned dielectric ceramic composition, exhibit superior high frequency characteristics, and have superior reliability under the environment of high temperature, high humidity, etc.
According to an aspect of the present invention, a dielectric ceramic composition comprises 100 parts by weight of a primary component comprising about 22 to 43 parts by weight of TiO2, about 38 to 58 parts by weight of ZrO2 and about 9 to 26 parts by weight of SnO2; and 3 to 20 parts by weight of glass containing at least B and Si.
Preferably, the dielectric ceramic composition further comprises about 10 parts by weight or less of NiO and about 7 parts by weight or less of Ta2O5. 
In a specified aspect of the present invention, the glass contains an alkali oxide, an alkaline-earth metal oxide, zinc oxide, Al2O3, B2O3 and SiO2, and has a composition represented by the following formulae relative to 100 weight %, on a weight % basis of the entity of the glass:
10xe2x89xa6SiO2xe2x89xa660;
5xe2x89xa6B2O3xe2x89xa640;
0xe2x89xa6Al2O3xe2x89xa630;
20xe2x89xa6EO xe2x89xa670 (wherein E: at least one element selected from alkaline-earth elements, Mg, Ca, Sr and Ba, and zinc (Zn)); and
0xe2x89xa6A2Oxe2x89xa615 (wherein A: at least one alkali metal element selected from Li, Na, and K).
Preferably, the dielectric ceramic composition further comprises about 7 parts by weight or less of CuO as an additive relative to 100 parts by weight of the primary component.
The present invention will be explained in detail as follows.
Because the dielectric ceramic composition according to the present invention contains about 3 to 20 parts by weight of the glass containing at least B and Si, relative to 100 parts by weight of the primary component, it can be fired at a temperature of about 1,100xc2x0 C. or less, and can be co-sintered with low resistance metals such as Ag and Cu. In the present invention, the TiO2 content is limited to the range of about 22 to 43 parts by weight relative to 100 parts by weight of the aforementioned primary component. When TiO2 content is less than about 22 parts by weight, the dielectric constant of the resulting dielectric ceramic is decreased. When the content exceeds about 43 parts by weight, the temperature coefficient of dielectric constant of the resulting dielectric ceramic becomes too large on the positive side.
The ZrO2 content is limited to the range of about 38 to 58 parts by weight. When the content is outside of this range, the temperature coefficient of the dielectric constant becomes too large on the positive side.
The SnO2 content is limited to the range of about 9 to 20 parts by weight.
When the content is less than about 9 parts by weight, the temperature coefficient of the dielectric constant of the obtained dielectric ceramic becomes too large on the positive side and the Q value is decreased. When the content exceeds about 26 parts by weight, the temperature coefficient of dielectric constant of the obtained dielectric ceramic becomes too large on the negative side.
When the glass content is less than about 3 parts by weight relative to 100 parts by weight of the aforementioned primary component, it is not possible to fire at a temperature of about 1,100xc2x0 C. or less. When the content exceeds about 20 parts by weight, the dielectric constant and the Q value of the obtained dielectric ceramic are decreased.
In the present invention, when about 10 parts by weight or less of NiO and about 7 parts by weight or less of Ta2O5 are added relative to 100 parts by weight of the primary component, the Q value can be improved. When the NiO content exceeds about 10 parts by weight or the Ta2O5 content exceeds about 7 parts by weight, on the contrary, the Q value of the obtained dielectric ceramic is decreased.
In the case in which the aforementioned glass component satisfies the aforementioned formulae, the sinterability at a low temperature of 1,100xc2x0 C. or less is further improved, the moisture resistance of the resulting dielectric ceramic is improved, and dielectric ceramics having high Q values and high dielectric constants can be more surely obtained.
In the case in which the SiO2 content is less than about 10 weight %, the moisture resistance of the obtained dielectric ceramic may be decreased and the Q value may be decreased. On the contrary, when the SiO2 content of the glass exceeds about 60 weight %, the softening temperature of the glass may be increased and then the sinterability may be decreased.
In the aforementioned glass composition, in the case in which the B2O3 content is less than about 5 weight %, the softening temperature of glass may be increased and then the sinterability may be decreased. When the content exceeds about 40 weight %, the moisture resistance may be decreased.
In the aforementioned glass composition, when the Al2O3 content exceeds about 30 weight %, the softening temperature of glass may be increased and then the sinterability may be decreased.
Furthermore, in the case in which the additive proportion of the aforementioned alkaline-earth oxide or ZnO is less than about 22 weight %, the softening temperature of glass may be increased and the sinterability may be decreased. On the contrary, when the proportion exceeds about 70 weight %, the moisture resistance and the Q value of the obtained dielectric ceramic may be decreased.
In order to improve low temperature sinterability, the addition of alkali to the glass is effective. When the additive proportion, however, of the alkali oxide exceeds about 15 weight %, the moisture resistance and the Q value may be decreased.
According to another aspect of the present invention, a ceramic multilayer substrate comprises a ceramic substrate including a dielectric ceramic layer comprising the aforementioned dielectric ceramic composition and a plurality of inner electrodes formed in the aforementioned dielectric ceramic layer of the ceramic substrate. In this ceramic multilayer substrate, the dielectric ceramic layer made of the dielectric ceramic composition according to the present invention is formed, and the plurality of inner electrodes are formed in the dielectric ceramic layer. Thus, the ceramic multilayer substrate can be sintered at a low temperature of about 1,100xc2x0 C. or less, the dielectric constant is high the Q value is high, and the temperature coefficient of the dielectric constant is small.
In the specified aspect of the ceramic multilayer substrate according to the present invention, a second ceramic layer having a dielectric constant which is lower than that of the inventive dielectric ceramic layer is laminated on at least one face of the dielectric ceramic layer.
In other specified aspect of the present invention, the plurality of inner electrodes are laminated with at least a part of the dielectric ceramic layer therebetween to constitute a monolithic capacitor.
In more specified aspect of the present invention, the plurality of inner electrodes are laminated with at least a part of the dielectric ceramic layer therebetween to constitute a capacitor, and coil conductors connected to each other to constitute a laminated inductor.
In another aspect of the present invention, a ceramic electronic part comprises the aforementioned ceramic multilayer substrate, and at least one electronic element mounted on the ceramic multilayer substrate and constituting a circuit together with the plurality of inner electrodes is provided. Preferably, a cap is fixed on the ceramic multilayer substrate so as to surround the aforementioned electronic element. More preferably, a conductive cap is used as the cap.
Specifically, the ceramic electronic part according to the present invention further comprises a plurality of external electrodes formed only on the bottom face of the ceramic multilayer substrate, and a plurality of through hole conductors electrically connected to the external electrodes and electrically connected to the inner electrode or electronic element.
According to another aspect of the present invention, a laminated ceramic electronic part comprises a ceramic sintered material made of a dielectric ceramic composition according to the present invention, a plurality of inner electrodes disposed in the ceramic sintered material, and a plurality of external electrodes formed on the outer surface of the ceramic sintered material, each of which is electrically connected to one of inner electrodes.
In the specified aspect of the laminated ceramic electronic part according to the present invention, the plurality of inner electrodes are disposed to be stacked with a ceramic layer therebetween to constitute a monolithic capacitor unit. In another specified aspect of the laminated ceramic electronic part according to the present invention, the plurality of inner electrodes in addition to the inner electrodes constituting the aforementioned monolithic capacitor unit include a plurality of coil conductors connected to each other to constitute a laminated inductor unit.